From: Jakub Jelinek <jakub@redhat.com>
To: Ulrich Drepper <drepper@redhat.com>
Cc: Glibc hackers <libc-hacker@sources.redhat.com>
Subject: [PATCH] Speed up sprintf
Date: Thu, 13 May 2004 11:15:00 -0000 [thread overview]
Message-ID: <20040513090306.GA5191@sunsite.ms.mff.cuni.cz> (raw)
Hi!
My http://sources.redhat.com/ml/libc-hacker/2003-05/msg00032.html
change apparently slowed down sprintf quite a lot on longer strings, if
buffer passed to sprintf is located in the first half of address space.
The problem is that the fix from last year for sprintf now sets write_end
to ~0L and if write_ptr is small enough, (ssize_t) (write_end - write_ptr)
is negative. This results in overflow being called for every single
character instead of doing a mempcpy.
The following patch seems to fix it, now sprintf at least on the sample
testcase I have on IA-64 is 30% faster than sprintf in glibc 2.2.4
(as opposed to being almost 4 times slower).
2004-05-13 Jakub Jelinek <jakub@redhat.com>
* libio/genops.c (_IO_default_xsputn): Avoid one overflow per char if
count is negative, yet write_ptr < write_end.
(_IO_default_xsgetn): Avoid one underflow per char if count is
negative, yet read_ptr < read_end.
--- libc/libio/genops.c.jj 2004-02-12 11:52:09.000000000 +0100
+++ libc/libio/genops.c 2004-05-13 13:02:15.715861960 +0200
@@ -447,10 +447,10 @@ _IO_default_xsputn (f, data, n)
for (;;)
{
/* Space available. */
- _IO_ssize_t count = f->_IO_write_end - f->_IO_write_ptr;
- if (count > 0)
+ if (f->_IO_write_ptr < f->_IO_write_end)
{
- if ((_IO_size_t) count > more)
+ _IO_size_t count = f->_IO_write_end - f->_IO_write_ptr;
+ if (count > more)
count = more;
if (count > 20)
{
@@ -462,9 +462,7 @@ _IO_default_xsputn (f, data, n)
#endif
s += count;
}
- else if (count <= 0)
- count = 0;
- else
+ else if (count)
{
char *p = f->_IO_write_ptr;
_IO_ssize_t i;
@@ -504,10 +502,10 @@ _IO_default_xsgetn (fp, data, n)
for (;;)
{
/* Data available. */
- _IO_ssize_t count = fp->_IO_read_end - fp->_IO_read_ptr;
- if (count > 0)
+ if (fp->_IO_read_ptr < fp->_IO_read_end)
{
- if ((_IO_size_t) count > more)
+ _IO_size_t count = fp->_IO_read_end - fp->_IO_read_ptr;
+ if (count > more)
count = more;
if (count > 20)
{
@@ -519,9 +517,7 @@ _IO_default_xsgetn (fp, data, n)
#endif
fp->_IO_read_ptr += count;
}
- else if (count <= 0)
- count = 0;
- else
+ else if (count)
{
char *p = fp->_IO_read_ptr;
int i = (int) count;
Jakub
next reply other threads:[~2004-05-13 11:15 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-05-13 11:15 Jakub Jelinek [this message]
2004-05-13 17:39 ` Ulrich Drepper
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